u 



sniVKYIN'!. 



SURVEYING. 



q 11, end of WTVI <A>U from it at remarkable point* toward* the 

 right an. I If ft hand alone that part of the road, be inewured. Again 

 at R let the (waring of the staff at D be observed ; let also the length 

 of K n, and of various offiietH along that line, be measured ; and 

 let it be supposed that the like prucen U continued n* far as may be 

 required. 



Each page of the field-book is then divided, lu below, into tl.r. -.- 

 columns by two parallel line* drawn down the page: and beginning at 

 the bottom of the column, the (several bearings of objects, the 1 

 of the sUlion-line*, and the several offeeU from tlioue lines are inserted, 

 in order, ascending towards the top of the page, the offset* being placed 

 on the right or left hand of the middle <-.>hmm, conformably to their 

 intuitions with respect to the station-line to which they belong. And 

 it is on this account that the several entries are made in succession 

 from the bottom upwards. The distances in the middle column 

 between the stations o and Q are reckoned from a; those between . { 

 and R are reckoned from q, and so on, each number in that column 

 expressing the distance up to the place in the station-line where the 

 offset whose length is given immediately on the right or left hand of 

 the number was taken. When it is required to determine by observed 

 bearing* the position of any object, as x, at a distance from the road, 

 those bearings are also inserted in the field-book at the stations, as Q 

 and R, where they were observed, and immediately under the bearing 

 of the next forward station. The mark O "> usually put to signify 

 the word " station." 



Fo*x or int FIELD-BOOK. 



The term " plotting " is applied to the process of laying down on 

 paper the plan of the ground which has been surveyed. If the survey 

 ha* been performed by the chain only, the several station-lines consti- 

 tute the sides of triangles extending over the whole of the ground ; the 

 lengths of those sides are determined by admeasurement, and in places 

 where they do not coincide with the roads, hedges, &c., offsets are 

 measured from the sides to the principal bends in those boundaries. 

 In order to " plot " the survey in this case, a proper scale of gradua- 

 tions, usually representing " chains " and "links," is chosen, and the 

 length of one of the station-lines taken from the scale being kid down 

 on the paper as a base, from the two extremities of it as centres, with 

 distances (taken from the scale) equal to the measured lengths of the 

 two sides, which with the base form the first triangle, area are de- 

 scribed to intersect one another ; this intersection being joined to the 

 extremities of the base by lines, the first triangle is constructed. Each 

 *ide of this triangle is then used as a base on which another triangle is 

 constructed with lines token from the scale equal to the measured 

 length* of the side*, and so on. After the triangulation is thus formed, 

 the offsets are laid down from them. This part of the process is accom- 

 plished by setting out with compasses upon each station-line, from one 

 of it* extremities, the several distances (taken from the scale) of the 



C' its at which the offsets were measured, drawing lines perpendicu- 

 y to the station-line at these points, and on them placing, from the 

 scale, the measured lengths of the offset* : lines joining the extremities 

 of these offset lines, either drawn by hand or with a ruler, will repre- 

 sent the lines of rands, the boundaries of fields, and the like. In order 

 to facilitate the operation of laying down the offsets from the station- 

 lines, the surveyor is usually provided with ivory scales graduated to 

 represent chains and links on the edges ; by laying an edge of such 

 scale ali ng the station line, with the zero of tin- graduations at one end, 

 the several distance* of the offset-lines from that extremity can be 

 marked on the line in succession; the scale may then be applied to 

 each offset-line, and the measured extent marked by means of the 

 graduations. 



But plotting scales are frequently made with graduations :il..ii.- tin- 

 edge*, and with a abort scale, also graduated on an edge, \\ lu.-li 

 posed at right angles to the length of the principal scale, and is capable 

 of being moved to any part of that scale by having une of its cxtiemi- 

 tic* cut BO as to slide in a groove formed in the dim-lion of tin 

 of the scale. The perpendicular scale is moved along the principal 

 scale to the graduation which denotes the place of the offset, and the 

 length of the latter is then marked by the graduations on tin- p< -rpen- 

 dicular scale. Since the offsets frequently occur on both nidi-* of the 

 station-line, the zero of the graduations on the perpendicular scale may 

 be at some distance from the edge of the principal seale, \\-hii -h is then 

 placed, not in coincidence with the station-line, but parallel to it .it 

 such a distance that tin- lero m.iy always be in tint line. By this 

 contrivance, which was first proposed by Major Uobe, the off*ei 

 the line may l>e marked, whether they be above or below it, without 

 displacing the principal scale. To find a convenient scale for plotting .1 

 survey, the length ami breadth of the whole may be couipi- 

 matively in order to ascertain the number of chains in such let. 

 breadth, and then the dimensions of the ]nper in inches bring known, 

 the number of chains in each inch may be formed by prop. 

 Plans of estates are usually made from scales of 2, 3, or 4 chains in an 

 inch, and the linear dimensions, on a plan made from a scale of 3 chains 

 in an inch, are equal to /(.,, of the actual dimensions on the ground. 



In important surveys, where the process consists in measuring a 

 1 i.-i-r linr, and observing with a theodolite the three angles of 

 triangle, the base is laid down on the paper from some scale as before ; 

 and at each of its extremities all the angles contained between the 

 base-line and visual rays from different objects to that extrem 

 set out by means of a protractor. The intersections of the 

 lines from the opposite extremities of the base determine the positions 

 of the objects, and form with the base the first triangles. The sides of 

 these triangles become then the bases of other triangles, and the angles 

 observed at the extremities of their sides must be set out by the pro- 

 tractor. If any of these lines should have been measured by the chain 

 on the ground, the sonstruction of the triangles by me\us of the 

 angles may be verified by measuring the lengths of such lines on the 

 scale by which the base-line was laid down. Offsets may also be laid 

 down as already described. 



But the practice in ordinary surveys is to observe by the " lock 

 angle," as before described, the bearings which the different station- 

 lines make with the meridian-line passing through one of the si 

 and to measure with the chain the length of each station-Iinr. 

 bearings and lengths, together with the offsets, are registered in the 

 field-book, and they are generally transferred to the paper in the fol- 

 lowing manner : 



A line, as N 8, is drawn in any convenient part of the paper, gene- 

 rally in a direction parallel to the right and left sides, to ivpre-eiit the 

 magnetic meridian ; and any point z is chosen in it, at which the 

 centre of the protractor is placed. Then the bearings, or angles made 

 with the magnetic meridian by the different station-fines, H K, K c, c L, 

 &c., are eet out by the graduations of the protractor about the point so 

 chosen, and lines, as z 1, z 2, z 3, &c., are drawn from this point through 

 the mark made on the paper on setting out each angle. These lines 

 are so numbered in order to indicate the particular station at which 

 each angle was observed. Then if the assumed point z on tin- mcridian- 

 line should be the place of the first station, the first line so drawn is in 

 the direction of the first station-line ; but if the assumed point is not 

 the first station, the place of this first station must be chosen on the 

 paper, as at H ; and a line drawn through it, parallel to z ], will be the 

 direction of the first station-line. Its extremity K, found by setting 

 out its length from the plotting scale, will be the place of the second 

 station. Through K a line is to be drawn parallel to z 2, and this will 

 be the direction of the second station-line, whose length K c must then 

 be set out as before. This process is to be continued till all the 

 station-lines have been laid down ; when, if the survey should have 

 been carried round the boundaries of a tract of ground, the second 

 extremity of the lost station-line will, provided the operations have 

 been accurately performed, coincide with n, the place of the first 

 station. From these lines the offsets must be set out as before 

 described. 



In order to set out the allotments of land in countries which, like 

 some parts of North America, are covered with wood, the surveyor 

 determines on the ground the position of a boundary-line comprehend- 

 ing an area of a square form, each side of which is six or eight miles in 

 length. One of these spaces, which constitutes a township, is usually 

 divided into squares of one mile on each side ; and again, these are 

 divided into squares of half or a quarter of a mile on each side. 



The boundary-line of the township is determined by measuring with 

 a chain a base-line six or eight miles in length, generally along one side. 

 of a square already marked out for some previous township ; and at 

 each extremity of this line carrying out one of equal length perpen- 

 dicularly to the base. Aline joining the fartl [ties of the 

 last lines completes thn square. In order to mark out the two sides 

 which are perpendicular to the measured base, a circumferentor, or a 

 large surveying-compass, furni---lu'd with plain " sights," and mounted 

 on a stand, is used. The bearing of the intruded line from the mag- 

 netic meridian being ascertained from the position of the lias,-, and the 

 instrument being set up at one extremity of that line, the line of the 



